New sales tax rate-need to back price down to come up with same total

Hello,

Seemed simple until I got into it. We created a manual invoice for a customer. We are now inputting that data into our computer but the sales tax has changed, so I would like to back down the price of the product to keep the sales tax amount correct and end total as I have already received payment for it.

The end total should be $5012.56.

If my sales tax rate is 8.375, what is the price of the product (organic compost) I am selling. It should be around $8 or $9 a ton.